This invention relates to maximum watthour demand meters and more particularly to such meters having a novel arrangement for compensation of meter disc loading when the meter is operated between active and inactive states of demand metering.
In accordance with electric utility billing practices, maximum watt demand billing is often required in addition to billing for total electric energy consumption. For purposes of multi-rate metering, a watthour demand register may include plural sets of dial indicators for separately indicating consumption during different times of the day. Accordingly, an associated maximum demand indicator may be activated only during on-peak load times experienced by an electric utility distribution system. The use of the aforementioned register to is provide customer penalty billing for electric usage during on-peak times and to encourage electric power usage during off-peak periods.
In U.S. Pat. No. 3,913,014, issued Oct. 14, 1975 and assigned to the assignee of this invention, an on-peak demand meter is described and claimed. A timing mechanism in the demand meter register actuates a cam to establish off and on demand measuring times. The demand interval timing motor is required to continuously drive the timing mechanism although the demand indicating gear train is deactivated during the off demand measuring periods.
In U.S. Pat. No. 2,145,069, a two-rate watthour demand meter includes two watthour energy consumption registers and a maximum demand indicator which effects operation of one of the energy consumption registers only when the power demand exceeds a predetermined level. The demand metering mechanism is operated continuously with the current demand pointer being periodically reset at the end of each demand time interval.
In U.S. Pat. No. 2,246,185 a two-rate watthour meter device or a chart recording watt meter device are disclosed utilizing a voltage electromagnetic section of the watthour meter movement having an integral timing motor. The voltage coil simultaneously provides flux for the stator of the timing motor and for the voltage metering fluxes. The patent notes that it is customary to space or magnetically shield the timing motor and the meter mechanism so as to prevent stray fluxes from the motor magnetic circuit from interfering with the metering fluxes and the measurement accuracy. The timing motor is intended for continuous use and is designed so that the motor fluxes do not interfere or contribute to the metering fluxes.
Accordingly, it is desirable to provide a maximum demand watthour meter with a simple, inexpensive and reliable means for compensating variable loading on the meter disc with activation and deactivation of the maximum demand metering operation. The variable disc loads caused by the demand gearing being periodically engaged and disengaged from the meter disc shaft requires compensation in the disc driving torque to provide accurate watthour and maximum watt demand measurements when such measurements are made periodically or intermittently rather than continuously.